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�y. Quarterly Groundwater Report iFrontier Transportation ' 0801-052 August 27, 2001 Page 4 ' No detectable concentrations of dissolved BTEX were identified in groundwater samples collected in August 2001 from monitoring wells MW-1, MW-2, MW-4, MW-5, MW-6, MW-7, ' MW-8, MW-9, MW-10, and MW-11 using EPA method 8020. Monitoring well MW-3 exclusively identified total dissolved BTEX at a concentration of 1,889 pg/L, an increase from 230 pg/L identified in April 2001. The potentiometric level dropped by 0.28' in well MW-3, which may have dissolved adsorbed BTEX still present in the soil. Total dissolved BTEX concentrations in MW-3, however, have attenuated by 77% since the maximum was identified as 8,350 }ig/L in March 1998 when groundwater rose to its shallowest depth recorded (7.l' bg). See Figure 5 for the recent dissolved BTEX Isoconcentration Map. MTBE was identified in groundwater from one monitoring well (MW-3) only in August ' 2001. Groundwater collected from monitoring well MW-3 identified an increase in MTBE concentrations from 250 pg/L to 1,300 pg/L, since the previous monitoring episode (April 2001) using EPA method 8260. The potentiometric level in MW-3 dropped 0.28' between the two ' groundwater monitoring episodes. The drop in the groundwater level may have dissolved adsorbed MTBE in the soil. However, MTBE concentrations have attenuated by 96% from the maximum concentration of 29,400 µg/L identified in MW-3 during March 1998. No detectable concentrations of oxygenates were identified from groundwater sample analysis of the remaining all ten monitoring wells using EPA method 8260 (See Appendix B). See Figure 6 for the recent MTBE Isoconcentration Map. ' 5.0) CONCLUSIONS AND RECOMMENDATIONS ' Based on groundwater sample analysis results, the dissolved TPH-d, TPH-g, TPH-m, BTEX, and MTBE plumes are spatially stable on-site and confined to the former UST location. No detectable concentrations of dissolved TPH-d, TPH-g, TPH-m, BTEX, and MTBE were ' identified in ten of the total eleven monitoring wells dedicated to the site. Dissolved TPH-g, BTEX, and MTBE were identified in monitoring well MW-3 exclusively located just east of ' former UST location. Attenuation of the above petroleum hydrocarbons has been identified in MW-3 since their respective recorded maximums identified in March 1998. BEII recommends that quarterly groundwater monitoring continue at the site until constant or decreasing dissolved petroleum hydrocarbon concentrations are observed. Groundwater samples will be analyzed for BTEX using EPA method 8020, TPH-d and TPH-g ' using EPA method 8015m, and oxygenates using EPA method 8260 in all future monitoring episodes as directed by the PHS/EHD. In addition, BEII requests that groundwater analysis for TPH-m will no longer be performed at the site. i